Many reasons exist for dispensing liquid adhesives, such as hot melt adhesives, in the form of a thin continuous filament with a controlled pattern. Conventional patterns used in the past have been overlapping patterns, more specifically a swirling pattern typically caused by impacting the filament with a plurality of jets of air. This is generally known as Controlled Fiberization™ or CF™ in the hot melt adhesive dispensing industry. Controlled fiberization techniques are especially useful for accurately covering a wider region of a substrate with adhesive dispensed as single filaments or as multiple side-by-side filaments from nozzle passages having small diameters, such as on the order of 0.010 inch to 0.060 inch. The width of the adhesive pattern placed on the substrate can be widened to many times the width of the adhesive filament.
Moreover, this technique is used to provide better control of the adhesive placement. Other adhesive filament dispensing techniques and apparatus have been used for producing a nonoverlapping vacillating pattern of adhesive on a substrate which, for example, may be a generally sinusoidal pattern or a stitching pattern in which the adhesive moves back-and-forth generally in a zig-zag form on the substrate.
In various types of manufacturing operations, it is necessary to bond thin elastic strands to one or more sheets of material, such as woven or nonwoven materials. This practice is especially prevalent in the area of hygienic article manufacture, such as during the manufacture of diapers. Diaper manufacturing involves the application of fiberized adhesives, including temperature and/or pressure sensitive adhesives, onto flat substrates and stretched elastic strands, for example, in the areas of the waistband, leg cuffs, and standing leg gathers of the diapers. In these situations, it has been common practice to dispense continuous adhesive fibers or filaments onto either single elastic strands or multiple elastic strands at the same time, either before or after the stretched elastic strand has been laid against the substrate, to bond the strand(s) to the substrate(s). In this manner, overlapping portions of the same substrate material may be bonded together with the elastic strand(s) secured therebetween or two distinctly different substrates may be bonded together with the elastic strand secured therebetween. This is a popular manner to elasticize specific areas of an article comprised of at least one flat substrate.
Controlled Fiberization techniques impart a generally back and forth motion to a dispensed filament of adhesive in the preferred form of a swirl by impacting the filament with a plurality of jets of air. This swirl generally takes the form of a repeated circular pattern when dispensed onto a substrate. When using CF nozzles to dispense swirling filaments of adhesive onto elastic strands, the continuous adhesive filament wraps itself around the strand(s) of elastic prior to joining the elastic strand(s) to the substrate.
Other adhesive filament dispensing techniques and apparatus have been used which involve dispensing a nonoverlapping vacillating, omega-shaped, or other types of back and forth patterns of adhesive on an elastic strand. Still other elastic strand securing methods include extruding a continuous layer of adhesive onto the strand after the strand has contacted the substrate. Various meltblowing techniques have also been used which essentially use randomly dispersed filaments of adhesive discharged onto one or more elastic strands either before or after the elastic strands have contacted the substrate.
Some of the continuing needs for improvement in this area of technology relate to achieving the necessary bond strength between the elastic strands and the substrates while at the same time transferring the desired elastic properties of the strands to the substrates. Another goal is to use as little adhesive as possible. In addition to undesirable cost increase, using too much adhesive tends to stiffen the substrate and reduce the elastic properties of the strand(s). This latter effect leads to reduced elasticity in critical areas of the diaper, such as the waistband, leg cuffs, and standing leg gathers. In addition, large fiber patterns may obstruct the communication of moisture between layers, such as between an inner layer and an absorbent outer layer.
For these and other reasons, it would be desirable to provide a method of securing one or more elastic strands to a flat substrate or sheet in a manner suitable for a high, speed manufacturing environment, while also achieving the necessary bond strength, creep resistance, efficient use of adhesive, and optimization of other desired characteristics of the resulting product.